Known oil supply apparatuses are disclosed in JP2003269186A (see columns 0017–0031, FIGS. 2–6) and JP2004143952A (see columns 0012–0016, FIGS. 1–3). With the configuration of the oil supply apparatus disclosed in JP2003269186A, oil, which is stored in an oil pan provided at a lower portion of an engine, is sucked by means of an oil pump through a strainer, and supplied to each part of an engine.
The oil supply apparatus disclosed in JP2003269186A is provided with a balancer housing in the oil pan in order to form a space into which an intrusion of the oil from the oil pan is prevented. A pair of balancer shafts is arranged in parallel relative to the space of the engine, and one of the pair of balancer shafts activates the oil pump. According to the oil supply apparatus disclosed in JP2003269186A, the balancer housing is formed with an oil discharge hole at a side portion thereof. The oil discharge hole is arranged at a position higher than an oil level of the oil in the oil pan. The oil flowed into the balancer housing is lifted by means of a drive gear or a balancer weight of the balancer shaft, and is fed back to the oil pan through the oil discharge hole.
With the configuration of the oil supply apparatus disclosed in JP2004143952A, the oil pan is attached to a lower crankcase, and is provided with a bottom separate wall portion in an interior space thereof. Further the oil supply apparatus includes a scavenge pump and a feed pump at a lower portion of the engine. The scavenge pump and the feed pump are driven by means of a common drive shaft. The oil, which is fallen after lubricating a bearing of the crankshaft and a piston, is collected in the bottom separate wall portion. Then, the oil is sucked by means of the scavenge pump through a suck pipe, and injected as an oil jet from a discharge pipe, and then the oil is fallen into the oil pan. Further, the oil stored in the oil pan is sucked by means of the feed pump through an intake pipe, and is passed through an oil filter, and then is supplied to each part of the engine.
With the configuration of the oil supply apparatus disclosed in JP2003269186A, the balancer shafts are arranged in an interior space of the balancer housing, and the oil in the balancer housing is lifted out during rotation of the balancer shafts. With such configuration, the balancer shafts may occasionally be applied with a rotational load caused by the oil. In order to prevent the balancer shafts from being applied with the rotational load caused by the oil, the oil supply apparatus disclosed in JP2003269186A sucks the oil in the bottom separate wall portion by means of the scavenge pump.
However, because the oil supply apparatus disclosed in JP2003269186A activates the scavenge pump and the feed pump by means of the common drive shaft, two pumps having a different function are arranged close to each other. Therefore, a structure of the pump, an oil passage, or the like, may occasionally be complicated.
A need thus exists for a oil supply apparatus, which reasonably activates the scavenge pump and the feed pump in the engine having a pair of balancer shafts.